Advisories

WDPN31 PGTW 072100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15E (NOLO) WARNING NR 
069//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 26.2N 157.7E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 1912 NM WEST-NORTHWEST OF JOHNSTON ISLAND
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 21 KTS
   SIGNIFICANT WAVE HEIGHT: 32 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
DESPITE MODERATE TO HIGH PERSISTENT EASTERLY VERTICAL WIND SHEAR
(VWS), ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS
AN ASYMMETRIC CENTRAL DENSE OVERCAST OBSCURING THE LOW-LEVEL
CIRCULATION (LLC). A 071756Z SSMIS 37GHZ MICROWAVE IMAGE REVEALS A
COMPACT, RESILIENT CORE, WITH A MICROWAVE EYE FEATURE, WHICH
SUPPORTS THE INITIAL POSITION WITH HIGH CONFIDENCE. THE CIMSS
HIGH-RESOLUTION COMBINED AMVS IMAGERY SHOWS THAT THE STRONG EASTERLY 
FLOW IS DEFLECTING AROUND THE CORE ALLOWING THE SYSTEM TO MAINTAIN AN
ORGANIZED LLC. THE INITIAL INTENSITY IS ASSESSED AT 60 KNOTS BASED
ON A BLEND OF THE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES,
CONSISTENT WITH THE CONVECTIVE STRUCTURE.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR)
ENTRENCHED TO THE NORTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T4.0 - 65 KTS
   PHFO: T4.5 - 77 KTS
   CIMSS ADT: 57 KTS AT 071740Z
   CIMSS D-MINT: 64 KTS AT 071505Z
   CIMSS D-PRINT: 57 KTS AT 071740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE WESTWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TROPICAL STORM (TS) 15E IS FORECAST TO TRACK
WEST-NORTHWESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF THE STR
THROUGH TAU 36, WITH A SHORT-LIVED PERIOD OF REINTENSIFICATION TO
65 KNOTS DUE TO DECREASING VERTICAL WIND SHEAR (VWS). AFTER TAU 48,
TS 15E WILL TRACK NORTHWARD TO NORTHEASTWARD WHILE ENCOUNTERING
INCREASING VWS ASSOCIATED WITH THE STRONG MIDLATITUDE WESTERLIES.
BY TAU 96, TS 15E WILL ACCELERATE AND BEGIN EXTRA-TROPICAL
TRANSITION (ETT) THEN COMPLETE ETT BY TAU 120 AS IT GAINS FRONTAL
CHARACTERISTICS AND TRACKS UNDER THE JET.    

MODEL DISCUSSION: THE PHYSICS-BASED MODELS INDICATE INCREASING
UNCERTAINTY AFTER TAU 36 AS THE SYSTEM RECURVES POLEWARD AND
ACCELERATES UNDER STRONG MIDLATITUDE WESTERLIES. THE TAU 48 TO TAU
72 CROSS-TRACK SPREAD RANGES FROM 170 TO 210NM, WITH A LARGE
ALONG-TRACK SPREAD AFTER TAU 72. RELIABLE INTENSITY GUIDANCE ALSO
SHOWS A LARGE SPREAD NEAR TAU 48, WITH HAFS-A PEAKING THE SYSTEM AT
94 KNOTS, WHICH APPEARS UNLIKELY DUE TO THE INCREASING VWS.
THEREFORE, THE JTWC INTENSITY FORECAST IS POSITIONED CLOSER TO ICNW
AND THE GOOGLE DEEP MIND PEAK INTENSITY VALUES. AI ENSEMBLE
SOLUTIONS SUPPORT THE JTWC FORECAST TRACK WITH MEDIUM CONFIDENCE. DUE 
TO THE PROXIMITY (ABOUT 700NM NEAR TAU 48) WITH TS 27W, THERE IS A LOW 
PROBABILITY FOR WEAK BINARY INTERACTION. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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